With the variable success of islet transplantation and the difficulty in predicting islet transplant success following islet isolation, it has become vitally important to gain a better understanding of islet cell health before and following transplantation. Currently, histologic and in vitro functional assays do not reliably predict islet transplant success. Proteomics technologies can examine the entire protein complement of cells, including post-translational modifications, and is ideally suited for detecting biomarkers of islet function. Novel proteomic approaches (Difference in Gel Electrophoresis and 2D LC MS/MS) will be used and developed to detect unique biomarkers in islet transplantation with a view to predicting islet transplant success and to monitoring ongoing islet transplant function. This proposal is divided into two parts: (1) an R21 phase which has a duration of two years and (2) an R33 phase which will be performed upon successful completion of milestones set forth for the R21. The sole specific aim of the R21 is to determine a panel of biomarkers that assess human islet viability for successful transplantation. This aim employs human islets transplanted into immunodeficient mice and will test the hypothesis that biomarkers in pre-transplanted islets can distinguish high grade (i.e. suitable for transplantation) from low grade islets. If biomarkers are successfully discovered then the R33 phase may ensue. Specific Aim I for the R33 is to determine whether biomarkers of islet viability successfully predict clinical islet transplant success. For this aim, we will analyze islet samples that are used for clinical islet transplantation, in collaboration with the University of Miami, to validate biomarkers identified in the R21 phase. This aim will test the hypothesis that newly developed biomarkers of human islet viability are valid in clinical islet transplantation. Specific Aim II will be to develop a rapid assay to detect putative biomarkers of islet viability that can be used by multiple islet transplant centers. Finally, Specific Aim III for the R33 is to determine the biomarkers of islet failure and death by assessing the plasma of patients that have undergone islet transplantation. This aim will test the hypothesis that biomarkers of islet stress and failure can be detected in the peripheral blood prior to islet graft failure. In summary, this proposal seeks to use powerful new proteomics platforms to discover biomarkers of islet viability prior to transplantation and also to discover plasma biomarkers that can assess the health of the islet graft following transplantation.